PCI Express® (Peripheral Component Interconnect Express, commonly abbreviated PCIe) is a computer bus standard defined by the PCI-SIG (PCI Special Interest Group) organization. Specifications of the PCIe standard are available on the PCI-SIG Web site, at www.pcisig.com/specifications/pciexpress/. PCIe is widely used both as a motherboard-level interconnect (to link motherboard-mounted peripherals) and as an expansion card interface for add-in boards. PCIe links are thus used, inter alia, to connect the host processor of a computer to a network interface controller (NIC) for purposes of network communications.
A PCIe link between devices can comprise between one and thirty-two lanes, which carry duplex serial data between the devices. In addition, a certain set of pins is allocated for management functions and providing electrical power to the peripheral device, as shown in the table below, taken from the PCI Express Card Electromechanical Specification, Revision 2.0 (Apr. 11, 2007), page 69:
TABLE IPCI EXPRESS CONNECTOR PINOUTPinSide BSide AComments1+12 VPRSNT1#Pulled low to indicate card inserted2+12 V+12 V3Reserved+12 V4GroundGround5SMCLKTCKSystem Management Bus (SMBus) and6SMDATTDIJTAG (IEEE 1149.1 testing) port pins7GroundTDO8+3.3 VTMS9TRST#+3.3 V10+3.3Vaux+3.3 VStandby power11WAKE#PERST#Link reactivation, fundamental reset
Wake-on-LAN (WOL) is an Ethernet computer networking standard that allows a host computer to be turned on by a network message. It permits the computer to automatically power down to a standby mode when it is not busy, and then power up when needed. The network message has the form of a “magic packet,” which is sent over the local area network (LAN) to the NIC of the computer that is to be awakened. The magic packet has a special format, which is recognized by the NIC as a “wake-up call.” Upon detecting a magic packet, the NIC asserts a wake signal to the host computer (such as the PCIe WAKE# signal listed in the table above), which initiates system wake-up.